Cyclooxygenase-2 (COX-2) is the inducible form of cyclooxygenase and catalyzes the rate- limiting step in the formation of prostaglandins from arachidonic acid. COX-2 expression and prostaglandin production increase markedly in neurons following a variety of stimuli including inflammatory mediators and excitatory synaptic activity. Previous studies in rodent models of ischemia have demonstrated that COX-2 activity significantly contributes to neuronal injury. Our initial studies have focused on identifying which prostaglandin receptors mediate COX-2 neurotoxicity. Although at least two prostaglandin receptors promote neuronal injury, our major finding has been that a larger group of prostaglandin receptors mediates an unexpected and significant protective effect in models of excitotoxicity and ischemia. Thus, the investigation of prostaglandin receptor pathways downstream of COX-2 has uncovered toxic as well as paradoxically protective signaling pathways, both of which are amenable to therapeutic targeting in models of ischemia. The research objective of this proposal is to examine the mechanisms of protection of one of these protective receptors, the PGE2 EP4 receptor. In this proposal, the cellular substrates and molecular mechanisms that mediate EP4 cerebroprotection in the murine model of transient focal cerebral ischemia will be investigated. Genetic strategies will be used to identify the cellular substrate(s) mediating protection by this receptor in ischemia. Separate experiments using pharmacologic and genetic approaches will test anti-apoptotic and pro-survival mechanisms mediated by this receptor. Successful completion of these studies will broaden our understanding of endogenous mechanisms of neurovascular protection in stroke, and establish the rationale for subsequent investigations in larger animal models of experimental cerebral ischemia, with the long term goal of therapeutic intervention in patients affected by stroke.